The female gametes of the brown alga Fucus, and the water mold Allomyces produce substances which attract the motile, unicellular male gametes. The goal of this proposed research is to determine the mechanism of the male gamete's response. The attractant of Allomyces has been characterized by others; we plan to identify and synthesize the attractant of Fucus. Possible chemical alterations of the attractants which are mediated by the male cells will be sought. If observed, the products will be characterized. Metabolic alterations induced in the male cell will be investigated. Initially respiration and steady state levels of cytochrome reduction in the absence and presence of the attractants will be measured. Steady state concentrations of the glycolytic and citric acid cycle intermediates will also be determined. We shall finally attempt to determine whether any observed metabolic responses arise from a direct interaction of the attractant with an intracellular component, or whether there is an indirect mechanism which involves a cell membrane receptor.